    [Patent document 1] JP-2007-71601 A (US 2007/0055444 A1)
There is known a navigation apparatus in a subject vehicle to learn a new road not registered in existing ready-made map data based on a travel locus or travel track of a moving object such as a vehicle. The road learning function is to prepare and store or recorded a new road (learned road) not existing in map data based on a travel track from a spot where a present position of the moving object separates from an existing road in the map data to a spot where the present position returns into an existing road in the map data, thereby learning a new road which has not been registered in the map data.
Incidentally, an in-vehicle navigation apparatus provides a route guidance method for a rotary intersection (i.e., a traffic circle, roundabout, rotary). For example, please refer to Patent document 1. Conventionally, the guidance for a rotary intersection uses an exit port number mode, which presents what number exit port after entering a rotary intersection should be used to exit from the rotary intersection, e.g., “please exit at the second exit path ahead.”
By the way, the above conventional rotary intersection guidance does not consider a guidance method for the case where the learned road acquired by the road learning function is connected with a rotary intersection existing in the map data. That is, there is a case where the conventional rotary intersection guidance applies to a rotary intersection where the existing road and the learned road acquired by the road learning function are intermingled in the map data, thereby causing various situations.
For instance, suppose that a learned road linked to a rotary intersection passes inside of the rotary portion. Traveling this learned road signifies traversing the rotary intersection. There is a possibility that a vehicle goes through a private road or a private site and takes a shortcut against a regulation. Therefore, it is not necessarily appropriate to carry out the same route guidance for such a learned road as that for another existing exit path.
In contrast, the above rotary intersection guidance using the exit port number mode may use the following assumption. That is, when the existing road and the learned road are intermingled as exit ports (exit paths) exiting from the rotary intersection, a series of exit port numbers may be assigned to an existing road and a learned road without considering the difference between the existing road and the learned road. Thereby, based on the thus assigned exit port numbers, the exit path guidance from the rotary intersection may be executed. Further, the learned road may be cancelled from the registration by a user when the learning result is unsuitable. In addition, a new exit path may be added as a learned road in the rotary intersection. In this case, each time a learned road is deleted from the rotary intersection or added into the rotary intersection, the exit port numbers that are used for the route guidance are changed. This may confuse a user.